During System on Chip (SoC) design, Network on Chip (NoC) prototyping is used for adapting NoC parameters to the application running on the chip. This prototyping is currently done using traffic generators which emulate the SoC components (IPs) behavior: processors, hardware accelerators, etc. Traffic generated by processor-like IPs is highly non-regular, it must be decomposed into program phases. We propose an original feature for NoC prototyping, inspired by techniques used in processor architecture performance evaluation: the automatic detection of traffic phases. Integrated in our NoC prototyping environment, this feature permits to have a completely automatic toolchain for the generation of stochastic traffic generators. We show that our traffic generators emulate precisely the behavior of processors and that our environment is a versatile tool for networks-on-chip prototyping. Simulations are performed in a SystemC-based simulation environment with a mesh network-on-chip (DSPIN) and a processor running MP3 decoding applications.